Electric resistance welding electrode holder for holding two electrodes in balanced force contact

ABSTRACT

A variable condition compensating and equalizing dual electrode holder having cam-surfaced pistons supporting the electrodes and a barrel cam coacting with the cam surfaces on the pistons. The pistons are resiliently extended by springs and one piston retracts upon contact until the other piston makes contact with the workpiece in advancing movement of the holder. This action is permitted by transverse movement of the barrel. Further inward movement of the pistons due to advancing movement of the holder locks the pistons in their different extensions against the barrel. Further advancing movement of the holder presses the electrodes into equal contact with the workpiece. Coolant circulation is provided by tubular pistons and coaxial tubes and transferring coolant across the holder body through the barrel cam cavity from side apertures in the tubular pistons.

United States Patent [72] inventor Robert B. Width Rochester, Mich.

211 AppLNo. 734,364

[22] Filed June 1,1968

[45] Patented Jan.26, 1971 [73] Assignee Tuftaloy Products, Inc.

Detroit, Mich. a corporation of Michigan [54] ELECTRIC RESISTANCEWELDING ELECTRODE HOLDER FOR HOLDING TWO ELECTRODES IN 2,976,599 4/1961Width ABSTRACT: A variable condition compensating and equalizing dualelectrode holder having cam-surfaced pistons supporting the electrodesand a barrel cam coacting with the cam surfaces on the pistons. Thepistons are resiliently extended by springs and one piston retracts uponcontact until the other piston makes contact with the workpiece inadvancing movement of the holder. This action is permitted by transversemovement of the barrel. Further inward movement of the pistons due toadvancing movement of the holder locks the pistons in their differentextensions against the barrel. Further advancing movement of the holderpresses the electrodes into equal contact with the workpiece. Coolantcirculation is provided by tubular pistons and coaxial tubes andtransferring coolant across the holder body through the barrel camcavity from side apertures in the tubular pistons.

ELECTRIC RESISTANCE WELDING ELECTRODE HOLDER FOR HOLDING TWO ELECTRODESIN BALANCED FORCE CONTACT This invention relates to electric resistancewelding means and in particular to electrode holders having twoelectrodes and which are capable of compensating for variableconditionsto urge both electrodes into substantially equal contact to producesubstantially equal welds.

When two electrodes are used to make two welds at the same time, theymust be pressed into substantially equal electrical contact with theworkpiece and theopposing base electrode or one electrode passes toomuch current and the other passes too little current resulting inextreme instances of burning out one weld and failing to make the other.Since the electric current follows the best conduction path, theelectrical contact of each electrode is critical. As the equality of theelectrical contact depends on the equality of the mechanical engagementof the conducting parts, the equality of the mechanical engagement oftwo electrodes on a single holder is critical.

The involved include the difference in thickness of workpieces,misalignment of tools, over and under seating of electrodes in theholder, difference in electrode length, mushrooming and other wear onelectrodes, bends in workpieces, and unevenness of the base electrode,inter alia. These differences need only be minute to greatly change theconductivity of one electrode relative to the other.

With the foregoing in view, it is a primary object of the invention toprovide a variable condition equalizing and compensating holder forholding two electrodes in substantially equal mechanical contact toeffect substantially equal electrical contact to make substantiallyequal welds.

An object of the invention is to provide a very compact compensatingholder so that little space is used and so that the electrodes may belocated close to one another.

An object of the invention is to provide a holder which jams its movingcompensating parts in solid electrical contact with one another prior toconducting welding current.

An object of the invention is to provide a holder which unjams after thewelds are made so as to have its compensating parts readily movable formaking the next welds.

An object of the invention is to provide coolant circulation meansassociated with the novel structure.

An object of the invention is to provide an very simple mechanism toobviate current conducting problems.

These and other objects of the invention will become apparent byreference of the following description of an equalizing and compensatingdual welding electrode holder embodying the invention taken inconnection with the accompanying drawing, in which:

FIG. 1 is a face elevational view of the holder seen in FIG. 3 in thedirection of the arrow 1, wherein the barrel cam and the transverse camtrack are seen through the transparent cover plate.

FIG. 2 is a cross-sectional view of the device shown in FIG. 3 taken onthe line 2-2 of FIG. 3.

FIG. 3 is a cross-sectional view of the device shown in FIG. 1 taken onthe line 3-3 thereof.

FIG. 4 is a partial cross-sectional view of the device as seen in FIG. 2showing a different compensating position of the parts showing thepistons in elevation; and

FIG. 5 is a cross-sectional view of the device seen in FIG. 1 taken onthe line 5-5 thereof with the barrel cam removed to show the rollertrack.

Referring now to the drawings wherein like numerals refer to like andcorresponding parts throughout the several views, the equalizing andcompensating dual electrode holder disclosed therein to illustrate theinvention comprises, a holder body having a threaded aperture 11 forsecuring the body 10 on a mounting stud 12, paired cylinders 14 and 15,and a transverse cavity 16 whose upper and lower defining wallsconstitute a cam track for a barrel cam. The cavity 16 partiallyinterrupts the cylinders 14 and 15.

A pair of pistons 18 and 19 lie in the cylinders 14 and 15 respectively.Each piston 18 and 19 has a notch 60, 61 in the location of the camtrack cavity 16 to form paired opposed top and bottom cam surfaces 2023,FIG. 4. A barrel 25 constituting a cam lies in the cavity 16 with itsperiphery extending into the notches 60,61 of the pistons 18 and 19inworking relationship with their cam surfaces 2023. Springs 26 and 27 arepositioned between the ends of the cylinders 14 and 15 and the tops ofthe pistons 18 and 19 respectively. The springs 26 and 27 resilientlyurge the pistons 18 and 19 downwardly in the cylinders 14 and 15 withtheir top cam surfaces 20 and 22 respectively normally in contact withthe barrel 25. The barrel 25 acts as a key to lock the pistons in theholder body 10.

The depth of the notches 60, 61 of the spacing of the cam surfaces 2023on the pistons 18 and 19, the dimension of the cam track cavity 16, andthe size of the barrel 25 are coordinated to each other to facilitaterelative axial movement of the pistons 18 and 19 relative to the barrel25 and transverse relative movement of the barrel 25 relative to thepistons 18 and 19, I

The outer ends of the pistons 18 and 19 have tapered sockets 30 and 31.Electrodes 32 and 33 are mounted in the sockets 30 and 31 of the pistons18 and 19.

When the holder 10 is retracted with the electrodes 32, 33 out ofcontact with the workpiece 34, the springs 14, 15 urge the pistons 18-l9downwardly with the top cam surfaces 20,

22 in contact with the barrel 25. This substantially centers the barrel25 and substantially equally extends the pistons 18, 19 and electrodes32, 33 outwardly of the holder body 10. In this condition the bottom camsurfaces 21, 23 are spaced from the barrel 25.

Under completely ideal conditions of actual equality, when the holder 10is advanced toward a workpiece 34, both electrodes 32, 33 contact theworkpiece 34 equally and move the pistons l8, 19 against the springs 14,15 equally until the bottom cam surfaces 21, 23 equally engage thebarrel 25 preventing further axial inward movement of the pistons 18,19, whereupon with further advancement of the holder 10, the electrodesare forced into substantially equal electrical contact with theworkpiece 34 to make substantially equal welds.

However, when these ideal conditions do not obtain, which is the casemuch more often, one electrode 32, 33 first contacts the workpiece 34and moves its piston 18, 19 axially inwardly of the holder body 10. Thusone bottom cam surface 21, 23 is moving axially inwardly in advance ofthe other and cams the barrel 25 transversely toward the other piston18, 19 bottom cam surface 21, 23. When the trailing cam surface 21, 23on the other piston 18, 19 contacts the barrel 25, further transversemovement of the barrel 25 is stopped and then further axial inwardmovement of the pistons 18, 19 is stopped as the barrel 25 is jammedtherebetween. Upon further advancement of the holder body 10 theelectrodes 32, 33 are forced into substantially equal engagement withthe workpiece 34 to make substantially equal welds.

When the holder body 10 is retracted from the workpiece 34 after thewelds are made both under equal and unequal conditions, the electrodes32, 33 exert no axially inward force and the springs l4, 15 move thepistons 18, 19 axially outwardly until the top cam surfaces 20, 22 againengage and center the barrel 25 with. the pistons 18, 19 again insubstantially equal axial projection. Thus the device automaticallycompensates and equ'alizes the various conditions between the workpiece34 and the electrodes 32, 33 each time welds are made and automaticallyreconditions itself after the welds are made to compensate and/orequalize the situation relative to the next welding operation.

Referring now to the novel coolant fluid circulation system, the pistons18, 19 may be axially hollow or tubular as shown to include internalaxial channels 40, 41 respectively. The

notches in the pistons 18, 19 forming the cam surfaces 20-23 maycommunicate through the tubular wall of the pistons 18,

19 and thus constitute communicating apertures in the location of thecam track cavity 16 or other suitable apertures in the pistons may beprovided. This facilitates coolant fluid transfer between the interiorchannels 40, 41 of the pistons l8, 19 through the cavity 16.

.Paired orifices 42, 43 in the holder body are equipped with a fitting44 and a hose 45 for supply and return of coolant fluid. Counterbores 46and 47 above the cylinders 14, communicate with the orifices 42, 43.Tubes 48, 49 are jam fitted in the counterbores 46, 47 and lie coaxiallyin the channels 40, 41 of the pistons 18, 19 with their bottom ends openand spaced from the base of the cavities 50, 51 in the electrodes 32,33.

Coolant fluid supplied to the orifice 42 travels through the tube 48 tothe electrode cavity 50, returns up through the coaxial piston channel40 to the notch 60, crosses through the cam track cavity 16 past thebarrel 25 to the notch 61 in the piston 19 and there enters coaxialchannel 41 of piston 19 and travels down the channel 61 to the electrode33 cavity 51 and returns up the tube 49 to the orifice 43 where itexits. The flow of the coolant fluid may, of course be reversed bysupply the fluid to the orifice 43 and returning it at the orifice 42.

O-ring seals 62, 63 on the pistons 18; 19 prevent fluid escape from thecylinders 14, 15 and an O-ring seal 64 at the cam track cavity 16prevents fluid escape between the body 10 and the fact plate 65.

While only a single preferred embodiment of the invention has been shownand described in detail, it is obvious that many changes may be made inthe various elements of the invention as to shape, size, detail andarrangement including fluid cooled and nonfluid cooled embodimentswithin the scope of the appended claims.

lclaim:

l. A compensating electrode holder for making electric re sistance weldswith two electrodes for substantially equalizing varying conditions atone electrode relative to the other electrode to effect substantiallyequal welds by making substantial equal engagement of both electrodesagainst a workpiece, comprising:

a holder body having paired cylinders and a transverse camtrack cavitybetween said cylinders:

a piston in each said cylinder, and a round barrel in said cavitybetween said pistons;

said pistons being relieved to form a lower cam surface on said pistonsbelow said round barrel relief on said pistons leading from said cavity;

said cam surface being adapted to engage said round barrel;

said device being so coordinated as to allow axial movement of saidpistons relative to each other and to said round barrel and to allowtransverse movement of said barrel relative to said pistons; saidpistons having outer ends beyond said holder body equipped with socketsfor mounting electrodes therein; said pistons being selectively movedaxially inwardly of said holder body when said holder body advanceselectrodes mounted on said pistons into engagement with a workpiece;

said round barrel allowing differentdistances of axial inward movementof said pistons by transverse movement of said round barrel of saidround barrel between said lower cam surfaces on said pistons so as toengage said lower cam surfaces at different rise points on said camsurfaces;

said round barrel when in engagement with both said lower cam surfacesof both said pistons being jammed therebetween preventing further axialinward movement of both said pistons securing said pistons andelectrodes in their so adjusted axial projection; and

said pistons, carn surfaces, and round barrel by relative movementbetween each other therebyallowing for different axial extension ofelectrodes mounted on said pistons to compensate different workpieceengagement conditions at the electrodes. i

2.1n a device as set forth in claim 1:

an upper cam surface on each said piston above said round barrel;

said pistons having innerends within said holder body;

a spring in each said cylinder between said inner end of each saidpiston and said holder body; and

said springs resiliently displaceably urging said piston upper camsurfaces against said barrel to roll said round barrel to center betweensaid piston to position said pistons outer ends at maximum axial outerprojection of said holder body.

3. in a device as set forth in claim 1:

said pistons being axially hollow; v

said holder body having fluid coolant inlet and outlet orifices andchannels; one said orifice and channel leading to one said cylinder andthe other said orifice and channel leading to the other said cylinder; Ii

a tube lying coaxially in each saidpiston with each said tube connectedto one said orifice and channel;

each said piston having a radial aperture communicating between itsaxial hollow interior and said cam track cavity of said holder body;

said coaxial tubes having bottom ,ends adjacent said piston sockets; i

coolant fluid fed into one said orifice and channel traveling down saidcoaxial tube to an electrode in said piston socket;

back up the associated said piston hollow interior to its radialaperture, through said radial aperture, cam track cavity and said radialaperture of the other said piston into its hollow interior; 7

down said other piston's hollow interior to an electrode mounted in saidother piston socket;

and back up said other pistons said associated coaxial tube to the othersaid channel and orifice of said holder body.

1. A compensating electrode holder for making electric resistance weldswith two electrodes for substantially equalizing varying conditions atone electrode relative to the other electrode to effect substantiallyequal welds by making substantial equal engagement of both electrodesagainst a workpiece, comprising: a holder body having paired cylindersand a transverse cam-track cavity between said cylinders: a piston ineach said cylinder, and a round barrel in said cavity between saidpistons; said pistons being relieved to form a lower cam surface on saidpistons below said round barrel relief on said pistons leading from saidcavity; said cam surface being adapted to engage said round barrel; saiddevice bEing so coordinated as to allow axial movement of said pistonsrelative to each other and to said round barrel and to allow transversemovement of said barrel relative to said pistons; said pistons havingouter ends beyond said holder body equipped with sockets for mountingelectrodes therein; said pistons being selectively moved axiallyinwardly of said holder body when said holder body advances electrodesmounted on said pistons into engagement with a workpiece; said roundbarrel allowing different distances of axial inward movement of saidpistons by transverse movement of said round barrel of said round barrelbetween said lower cam surfaces on said pistons so as to engage saidlower cam surfaces at different rise points on said cam surfaces; saidround barrel when in engagement with both said lower cam surfaces ofboth said pistons being jammed therebetween preventing further axialinward movement of both said pistons securing said pistons andelectrodes in their so adjusted axial projection; and said pistons, camsurfaces, and round barrel by relative movement between each otherthereby allowing for different axial extension of electrodes mounted onsaid pistons to compensate different workpiece engagement conditions atthe electrodes.
 2. In a device as set forth in claim 1: an upper camsurface on each said piston above said round barrel; said pistons havinginner ends within said holder body; a spring in each said cylinderbetween said inner end of each said piston and said holder body; andsaid springs resiliently displaceably urging said piston upper camsurfaces against said barrel to roll said round barrel to center betweensaid piston to position said pistons outer ends at maximum axial outerprojection of said holder body.
 3. In a device as set forth in claim 1:said pistons being axially hollow; said holder body having fluid coolantinlet and outlet orifices and channels; one said orifice and channelleading to one said cylinder and the other said orifice and channelleading to the other said cylinder; a tube lying coaxially in each saidpiston with each said tube connected to one said orifice and channel;each said piston having a radial aperture communicating between itsaxial hollow interior and said cam track cavity of said holder body;said coaxial tubes having bottom ends adjacent said piston sockets;coolant fluid fed into one said orifice and channel traveling down saidcoaxial tube to an electrode in said piston socket; back up theassociated said piston hollow interior to its radial aperture, throughsaid radial aperture, cam track cavity and said radial aperture of theother said piston into its hollow interior; down said other piston''shollow interior to an electrode mounted in said other piston socket; andback up said other piston''s said associated coaxial tube to the othersaid channel and orifice of said holder body.